Impact matrix printers are well known in the art and are typically used as high speed printers in conjunction with electronic data processing systems or digital communications systems. Impact matrix printers known in the art include serial wire matrix printers, bar matrix printers and helix matrix printers. In such existing impact matrix printers, a character is formed from the visual impression of dots or squares on the print record arranged in accordance with a matrix character pattern.
An illustration of the operation of an existing impact matrix printer may be provided by describing a serial wire matrix printer. A serial wire matrix printer has a printhead comprised of a column of print wires stepped serially across a print record to print a line of characters. Electrical signals derived from a data processing or digital communication system control the selective firing of a print hammer, causing selected wires in the printhead to be driven against an inked ribbon to form an inked impression upon the print record. Character configuration information for a font of characters formed in accordance with a matrix character pattern is placed in storage, and the electrical control signals activate the print hammers firing the print wires in accordance with the character configuration information. Upon completion of a line of print, the print record is advanced to the next line and the printhead is returned to its starting position.
Wire matrix printers now generally utilize a circular impact wire printing element in conjunction with a 7.times.7 restricted matrix character pattern to form the character images of a font of characters. The total character matrix is ten positional units wide, providing three positional units between adjacent characters. The matrix character pattern restriction is such that any dot defined as "on" must be horizontally adjacent to an "off" dot, so that no two horizontally adjacent dots can exist within the character matrix for the font of characters. While a single dot may exist in any one of the seven discrete positions along a row, this matrix pattern allows for a maximum of only four dots to exist within one horizontal row. This pattern guarantees a minimum defined "off" time to allow for print hammer recovery, which allows the printhead to move at twice the speed it would if each of the seven dots in the 7.times.7 matrix was printed.
It is of course advantageous to operate a printer at the highest print speeds possible without a reduction in print quality. Current high speed matrix printers are limited by the mechanical restraints of the incremental actuation of the print hammers of the matrix printer fired in response to electrical control signals. A need has thus arisen for increasing the speed of an impact matrix printer while maintaining print quality.
In accordance with the present invention, a matrix printer includes a printhead having an elongated impact member and a matrix character pattern which requires fewer strokes to form a character. The horizontal character matrix for the font of characters is divided into a larger number of time increments in which the impact member covers more of the timing increments to increase the speed of printing. The total character matrix is twenty units wide and has thirteen adjacent units within the matrix as possible positions for firing the print hammer. A storage element is used to store the basic print hammer firing information for forming each of the characters. The restricted matrix pattern restricts the hammer from firing any sooner than six positional units or not more than three times per character. Thus, the present invention enables a matrix printer to operate at an increase in speed over existing matrix printers while maintaining the clarity of the printed characters.